The present invention relates to a thermal analyzer and, in particular, relates to a thermal analyzer having means for rigidly positioning the elements thereof.
In general, thermal analyzers are instruments which measure the thermal absorption or emission parameters of a sample material. These parameters characterize the sample material. In practice, these parameters are most characteristic of materials when obtained during phase transitions of the sample material, i.e. when the sample material changes from one physical state, for example a solid, to a second physical state, for example a liquid. It is well settled that a phase transition is either an exothermic process or an endothermic process. Thus, the thermal energy absorbed or emitted by a sample material during a phase transition has become a widely used means for recognizing and identifying materials. In order to correctly identify a sample material, it is necessary to accurately measure the temperature changes of the sample material during the phase transition. This is usually accomplished by comparing the time rate of change of the sample temperature with the time rate of change of the temperature of a reference material when both are subjected to the same temperature profile. The reference material is selected from materials having known thermal characteristics. Both the sample and the reference are then heated according to a preselected temperature profile and the temperatures thereof are monitored. From this information, the thermal characteristics of the sample material can be obtained and the material accurately identified.
One conventional thermal analyzer is known as a differential thermal analyzer and includes a pair of double bore ceramic columns, or tubing upon which sample and reference cups are respectively located. Each cup is contacted by a thermocouple, the electrical connections to which can extend through the ceramic support columns. Since the critical measurement in a differential thermal analyzer is the temperature difference, particularly during the phase transition of the sample, between the sample and reference materials, and further, since these receptacles are enclosed in a containment member having a rather small volume of an ambient atmosphere, the relative position of the columns and the receptacles thereon is extremely important. If, during a particular measurement, for any reason, the relative position of the columns change, the entire thermal conditions within the containment member also change, i.e. the thermal system becomes dynamic rather than static. The perturbations so introduced are particularly detrimental because, as previously mentioned, the containment member encloses a relatively small volume. For these reasons it is understood that the thermal gradient distribution within the volume is quite sensitive to even a small relative movement of any of the components within that containment volume.
In addition to the pair of support columns, there is often a purge tube member extending within the containment member which can be utilized to provide a particular atmosphere therein during the analysis. The tube, when present, becomes an integral part of the interactive thermal gradient within the containment member, and thus must also be physically and thermally stable.
Presently, a conventional analyzer includes a column support member extending from a base plate, which support member has at least a pair of holes drilled therethrough through which the columns extend. Since the support columns are generally cylindrical, this arrangement results in only a single point of tangential contact between each column and its respective hole in the support member. Thus, the distance between the columns, and as a result, the distance between the sample and reference cups, can vary and thereby introduce unacceptable errors in the resultant measurements. Of course, any movement of the purge tube likewise results in erroneous measurements.